Selective conjugate addition to zerumbone and transannular cyclization of its derivatives
作者:Kouichi Ohe、Koji Miki、Shin-ichi Yanagi、Takumi Tanaka、Seiji Sawada、Sakae Uemura
DOI:10.1039/b004284f
日期:——
Some chemical transformations of zerumbone (1) isolated from rhizomes of Zingiber zerumbet Smith have been described. Regioselective addition of benzenethiol and benzeneselenol to the Δ1,2 double bond of 1 occurs in the presence of tetra-n-butylammonium fluoride (TBAF) as a catalyst to give 1-phenylthio and 1-phenylseleno adducts 2a and 2b, respectively, with moderate diastereoselectivity. In the presence of BF3·OEt2 the reaction of 2a and 2b with trimethylsilyl cyanide proceeds in 1,4-addition fashion to give the corresponding 5-cyano silyl enolates 3a and 3b, respectively. Desilylation of 3a and 3b with HF·pyridine provides (8E)-5-cyano-2,6,6,9-tetramethyl-1-phenylthiocycloundec-8-en-3-one (5a) and (8E)-5-cyano-2,6,6,9-tetramethyl-1-phenylselenocycloundec-8-en-3-one (5b) as a single diastereoisomer, respectively. Treatment of 2a and 2b with TiCl4 affords compounds with a bicyclo[5.3.0]decane skeleton, 6a and 6b, respectively, as trans-fused isodaucane derivatives via a transannular reaction between C-4 and C-9 of 2 followed by rearrangement. Palladium-mediated transannular reaction between C-4 and C-9 of 3b yields 7b with a bicyclo[5.4.0]undec-8-ene skeleton. Brønsted acid-catalyzed transannular reactions between C-3 and C-8 of 5a and 5b afford compounds with bicyclo[5.4.0]undecane skeletons 8a and 8b. A lithium enolate of (1Z)-5-cyano-8,9-epoxyzerumbone 10/10′ derived from 5b gives compounds with tricyclic skeletons, 11 and 12, by a transannular reaction between C-4 and C-8. Compounds 11 and 12 involve the carbon skeleton of 5,8-fused bicyclic natural sesquiterpene, asteriscane. Some molecular structures of key intermediates and products have been characterized by X-ray crystallography.
有人描述了从 Zingiber zerumbet Smith 根茎中分离出来的 zerumbone(1)的一些化学变化。在四正丁基氟化铵(TBAF)作为催化剂的存在下,苯硫醇和苯硒醇与 1 的 Δ1,2 双键发生区域选择性加成反应,分别生成 1-苯硫基和 1-苯硒基加合物 2a 和 2b,具有适度的非对映选择性。在 BF3-OEt2 的存在下,2a 和 2b 与三甲基硅基氰化物发生 1,4 加成反应,分别生成相应的 5-氰基硅烯醇 3a 和 3b。用 HF 吡啶对 3a 和 3b 进行脱硅处理,可分别得到 (8E)-5-cyano-2,6,6,9-tetramethyl-1-phenylthiocycloundec-8-en-3-one (5a) 和 (8E)-5-cyano-2,6,6,9-tetramethyl-1-phenylselenocycloundec-8-en-3-one (5b)单非对映异构体。用 TiCl4 处理 2a 和 2b,通过 2 的 C-4 和 C-9 之间的反annular 反应,然后进行重排,分别得到具有双环[5.3.0]癸烷骨架的化合物 6a 和 6b,它们是反式融合的异十二烷衍生物。钯介导的 3b 的 C-4 和 C-9 之间的反annular 反应产生了具有双环[5.4.0]十一-8-烯骨架的 7b。5a 和 5b 的 C-3 和 C-8 之间在布氏硬度酸催化下发生反annular 反应,生成具有双环[5.4.0]十一烷骨架的化合物 8a 和 8b。由 5b 生成的 (1Z)-5-cyano-8,9-epoxyzerumbone 10/10′ 的锂烯醇盐通过 C-4 和 C-8 之间的反烷反应生成了具有三环骨架的化合物 11 和 12。化合物 11 和 12 涉及 5,8-融合双环天然倍半萜--紫檀烷的碳骨架。一些关键中间体和产物的分子结构已经过 X 射线晶体学鉴定。